A hybrid structure in a construction machine such as a power shovel uses, for example, an excess output of an engine to rotate a generator for electric power generation. Then, the generated electric power is stored in a battery and the electric motor is driven by the electric power stored in the battery to actuate an actuator. Also, discharge energy from the actuator is used to rotate the generator for electric power generation. Then, similarly, the generated electric power is stored in the battery, and the electric motor is driven by the electric power of the battery for actuation of the actuator.
In a power shovel or the like, even when an actuator in a work mechanical system is stopped, the engine is maintained in a rotating state. In this event, since a pump rotates together with the engine, the pump discharges so-called standby flow rate.
[Patent Literature 1] JP-A 2002-275945